William O'Connell was born in Lowell, Massachusetts, to John and Bridget (née Farrelly) O'Connell, who were Irishimmigrants. The youngest of eleven children, he had six brothers and four sisters. His father worked at a textile mill and died when William was four years old.[1] During his high school career, he excelled at music, particularly the piano and organ.[1]

O'Connell was named Coadjutor Archbishop, with right of succession, of Boston, and Titular Archbishop of Constantina on February 21, 1906. As coadjutor, he served as the designated successor of Archbishop John Williams, who was then in declining health. He later succeeded Williams as the second Archbishop of Boston upon the latter's death on August 30, 1907.

On November 27, 1911, O'Connell became Boston's first Archbishop to become Cardinal, and was given the title of Cardinal-Priest of S. Clemente.[3] O'Connell was late to two papal conclaves in a row, in 1914 and 1922, due to having to cross the Atlantic Ocean in the slower transportation of the day. He made a protest to Pope Pius XI, who in response lengthened the time between the death of the Pope and the start of the conclave. O'Connell was able to participate in the subsequent 1939 conclave, although by that time air travel was available.

O'Connell favored a highly centralized diocesan organization, encompassing schools, hospitals, and asylums in addition to parishes. O'Connell wielded immense political and social power in Massachusetts, earning him the nickname, "Number One."[2] For instance, he was responsible for defeating a bill to establish a state lottery in 1935, and for defeating a referendum liberalizing state birth control laws in 1942.[2] The only politician who had anywhere near O'Connell's political clout was Governor (and future U.S. President) Calvin Coolidge, but even Coolidge picked his battles carefully, preferring to ignore the Archbishop whenever possible. In the years leading up to the Second World War O'Connell became a powerful force for the neutralists in trying to keep the United States out of World War II, in the pre-Pearl Harbor era.

He also condemned crooning, saying, "No true American man would practice this base art. Of course, they aren't men...If you will listen closely [to crooners' songs] you will discern the basest appeal to sex emotion in the young."[7]

He was also decidedly non-ecumenical. "In 1908 during ceremonies commemorating the 100th anniversary of the establishment of a Roman Catholic diocese in the Puritans' Boston, Archbishop William Henry O'Connell ... set the tone for the fast-growing church's next phase [by stating] "[t]he Puritan has passed. The Catholic remains." ([1]). :

From 1907 to 1944, William Henry O'Connell was Archbishop of Boston. This was the period when the American Catholic Church, so to speak, came of age. Churches, schools, convents, and hospitals were being built, quite literally, by the dozen. Thousands of children were enrolled in parochial schools, where they were taught by nuns and brothers. Priests were ordained each year by the dozen, and seminaries were built to accommodate the growing number of vocations. Some have called this the golden age of American Catholicism.

Nowhere was this more seemingly true than in Boston under O'Connell's leadership. Political leaders referred to him as "Number One", and sought his approval before taking action on a particular issue. And O'Connell loved every minute of it. One contemporary described him as a "battleship in full array."

O'Connell's young nephew, Msgr. James P. O'Connell, who served as chancellor of the archdiocese, had secretly married in 1913 and was leading a double life. The marriage was discovered and brought to the attention of the Vatican by certain of O'Connell's clerical enemies who deeply resented his rise to power. The relationship between uncle and nephew appears to have been permanently severed when Msgr. O'Connell was removed from office and from his priestly duties in 1920. The results may have been beneficial for all concerned, as the marriage of James O'Connell endured until his death in 1948, survived only by his widow, who died in 1969. The historical record as to what the Cardinal knew and when he knew it is unclear.[9][10]

In 1915, O'Connell fabricated autobiographical material, an attempt which was successful until 1987. James M. O'Toole discovered that O'Connell's volume of published letters,[11] which O'Connell claimed to have written in the time period indicated by the volume's title, were, in fact, written over a short period and expressly for the purpose of publication.[12] O'Toole has also acknowledged that others who had researched and written on the subject of the letters in 1975 had found the dates on the letters to be "suspect".

In the early 1940s when Frances Sweeney, editor of the Boston City Reporter, criticized O'Connell for his passivity in the face of rampant antisemitism in Boston, O'Connell summoned Sweeney to his office and threatened her with excommunication.[13][14][15]

On July 20, 2011 workers for the Catholic Cemetery Association of the Archdiocese of Boston began removing the Cardinal's remains from Boston College's campus and placed them in a temporarily unmarked grave at St. John's Seminary instead of Saint Sebastian's School. This was in accord with a deal struck between the descendants of the late Cardinal and the Archdiocese of Boston. A spokesman stated that "a proper marker" will be placed, with a full memorial ceremony, in the fall.[needs update][17]

His 36-year-long tenure was the longest in the history of the Archdiocese of Boston. He was the second-to-last surviving cardinal of Pope St. Pius X behind Gennaro Granito Pignatelli di Belmonte, and remains at present the third-longest serving American cardinal behind James Gibbons and William Wakefield Baum. In his book, Boston Catholics - A History of the Church and Its People, Thomas O'Connor, university historian at Boston College, O'Connell's alma mater, notes that during O'Connell's tenure as head of the Archdiocese of Boston, the number of women in religious life increased from 1567 to 5459; the number of parishes increased from 194 to 322; the number of churches increased from 248 to 375; the number of diocesan priests increased from 488 to 947; the archdiocese was operating 3 Catholic hospitals. At page 208 of Boston Catholics, O'Connor writes: "It was under O'Connell's influence too, that the Catholic Church in the Archdiocese of Boston assumed a conceptual solidarity and impressive visibility that it had never seen before and would never see again."

In Henry Morton Robinson's best-selling 1950 historical novel, The Cardinal, the Archbishop of Boston in the exact time frame as O'Connell's term in office is named "Lawrence Cardinal Glennon". Robinson's physical descriptions of Glennon, his massive Diocesan building program, his arriving late for two Papal conclaves in Rome, while eventually making it in time for a third, his popular description as "Number One" and many other details of the Glennon character exactly correspond with O'Connell's career and personality. The "Cardinal" of the title, however, is a young priest who serves as Glennon's secretary, only to eventually rise to the rank of Cardinal himself.[citation needed]

^William O'Connell. The letters of His Eminence William Cardinal O’Connell, Archbishop of Boston: vol. 1. From college days 1876 to Bishop of Portland 1901. (Cambridge, Massachusetts: Riverside Press, 1915.)

Peters, Walter H. The Life of Benedict XV. 1959. Milwaukee: The Bruce Publishing Company. Peters writes of the Vatican meeting of Pope Benedict XV and Cardinal O'Connell, over the scandal of his nephew's marriage.